802.16: A Look Under the Hood

802.16 promises to deliver true broadband speed wirelessly, but when will products be available and how important a role should the so-called WiMAX standard play in your future network plans? Join Beth Cohen and Debbie Deutsch as they continue their in-depth look at the wonderful world of WiMAX.

By enabling quick and relatively inexpensive deployment of broadband services infrastructure, the IEEE 802.16 standards for wireless broadband access have the potential to finally address the long-standing “last mile” problem that has plagued the data and telecom carrier industries. In Part 1 of our in-depth look at 802.16, we discussed how the new technology could be utilized and what was happening in the industry. Now let's delve into the nitty-gritty details of how the standards work and what data networking services they enable.

In addition to the physical layer discussed in Part 1, 802.16 defines a Media Access Control (MAC) layer. The capabilities of this layer allow 802.16 to support a wide array of data networking services, including many services that are already familiar to corporate and residential users using copper or fiber networks.

Because they provide the basis for these services, support for both ATM and packet operations was a requirement in the 802.16 design. ATM is important because of its role in telecom carrier infrastructure. For example, ATM is often used to support DSL services. ATM is also widely used to support voice transmissions. When it comes to packet operation, 802.16 supports all of the “usual suspects,” including IPv4, IPv6, Ethernet, and VLAN services.

802.16 accomplishes all of this by dividing its MAC layer into separate sublayers that handle different services, provide common core functions, and implement wireless privacy. Overall, this design gives 802.16 both flexibility and efficiency at the same time.

The convergence sublayers map the different services into the core MAC common part sublayer. In addition to relating service data units to MAC connections, the convergence sublayers are responsible for decisions about bandwidth allocation and QoS. They also embody functions to get the most efficient use (maximum effective bits transmitted and received) out of the radio frequencies themselves.

The common part sublayer is connection-oriented. All services, even connectionless services such as Ethernet and IP, are mapped into a MAC connection. The common part sublayer includes mechanisms for requesting bandwidth, including bandwidth on demand — a very attractive option for many carriers.

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